Taxonomic Hierarchy

Common Name (Official / AAS)

Other Common Names

Black Widow, Hourglass Spider, Shoe Button Spider

Author

Author of species name: Christian Fabricius. First year published: 1775, as Aranea mactans.

Pronunciation

lah-tro-DEK-tuhs MACK-tans

Meaning

Latrodectus is Greek for “biting in secret” (Cameron 2005); this refers to the painlessness of the initial bite and the fact that it often goes unnoticed until symptoms present. In Latin, mactans means “sacrifice, slaughter, destroy”.

Identifying Traits of Latrodectus mactans

Size

Female Primary Colors

Male Primary Colors

Eyes

Total of eight eyes; when viewed from the front, appears as two horizontal rows of four. The lateral eyes are completely separated from each other, which is a feature that can be used to distinguish true “widows” (genus Latrodectus) from the “false widows” (genus Steatoda). The secondary eyes may appear white or silver because of a light-reflecting, crystalline structure inside them called a “tapetum.” In spiders, the anterior median eyes (middle pair in the bottom row) are considered the primary eyes, while the others are considered “secondary.”

Legs

Front pair of legs is longest, third pair shortest, typical of the family Theridiidae. Legs are long in proportion to body and lack obvious spines. In adult female, legs entirely black; in immature females and males, the legs are banded in black and brown. Tarsi (tips of legs) have 3 claws.

Body

Abdomen of mature female is usually globose (much larger than the cephalothorax) and is entirely jet black and shiny (rarely dark chocolate brown) with a distinct red “hourglass” marking on the underside. There is also usually a red spot behind the spinnerets. Sometimes there may be a line of red spots and/or stripes down the center of the top of her abdomen. Females that have recently laid eggs may appear wrinkled and emaciated. Abdomen of mature male is smaller, more oval, and tapered toward the rear. They have several ornate white and red markings on the top (dorsal) side and a red or orange “hourglass” marking on the underside. Immature females resemble males, gradually losing their pale markings as they continue to age. Freshly hatched black widow spiderlings are mostly white, believe it or not, and turn darker with each molt. By the time they are dispersing from the mother’s web, which is fairly soon after they’ve left the egg sac, they will be reddish in color with small black and white blotches. They still possess an hourglass mark, even at a young age.

Range of Latrodectus mactans

Latrodectus mactans can be found in the following states, provinces and territories across the United States and Canada. Our current understanding of each spider's distribution is drawn from numerous scientific publications and online spider submissions, in order to be as accurate as possible. It is important to remember that spiders do not adhere to the territorial lines decided on by humans, therefore these ranges are subject to change.

Important Range Notes

This species is less common in the more northern parts of its range, where the “Northern Black Widow” (Latrodectus variolus) begins to replace it.

Canada

Additional Information

Habitat

This species is reclusive and seeks extremely protected spaces where it builds its retreat; lives in close proximity to man-made structures as well as further away in more natural habitats. By day, the spider is safely ensconced in its retreat, venturing into the body of its web only under cover of darkness. The slightest disturbance of its web by a large animal sends it dashing back into its lair. Be careful handling objects that have been undisturbed outdoors for long periods, such as children’s toys and playground equipment, gardening pots, lawn furniture, buckets, trash cans, etc. This spider may sometimes be accidentally transported to other places outside its natural range, occasionally in fruit or plant shipments.

Web

This species spins an extensive, tangled, three-dimensional “cobweb” snare. The threads are extremely strong and elastic, and can be plucked like guitar strings without breaking. The lines anchored to the ground (or lowermost substrate) are the trap lines. Insects, or other spiders, that trip the lines become entangled. The rebounding silk yanks the victim into the body of the web where the spider apprehends it. Flying insects may also be intercepted by the body of the web. During the day, or when being disturbed, the spider usually hides deep in a funnel-like retreat beneath a boulder, inside a rodent burrow, or in a crevice. The spider will usually hang upside down in the body of its web at night, awaiting prey. This is a good time to use a flashlight and check for the red “hourglass” symbol that is distinctive to black widows.

Season

Mature individuals may be found at nearly any time of year. Mature females can live well over a year after reaching maturity.

Food

Prey is almost any insect or spider or other small animal, including very small vertebrates that becomes entangled in the snare.

Lifecycle

Egg sacs are oval white or pale gray objects, about 8-12 mm in diameter, which are suspended in the web. A single female may have 3 or 4 egg sacs in her web at one time, each containing anywhere from 100-900 yellow eggs (Kaston 1948). On average, the female can produce 9 to 15 egg sacs in her 1-2 year lifetime. The spiderlings that emerge from the eggs are essentially white, but turn a salmon color with dark and light stripes after one molt. They darken more as they mature, but males mature faster than females, so retain pale and/or colorful markings into adulthood. Contrary to popular legend, male widows are not always consumed by the female after copulation. Normally, if she is already well fed, the male gets away clean and may even go on to mate with additional females (Breene & Sweet 1985). With all spiders, it is always a possibility that the female might eat their mate, though, especially if he doesn’t exit the web soon enough.

Remarks

This species is a potentially dangerous spider, though it is extremely timid and non-aggressive. Its venom is neurotoxic, and quite virulent. While there is no “typical” reaction to a bite in humans, it can be an excruciating experience if venom was injected (as opposed to a “dry” bite). The major muscle groups are usually affected, causing extreme cramping, with subsequent deep bruising. Antivenin is available, derived from horse serum, but because of the possibility of “serum sickness,” it is administered only in those very rare instances when the bite is life-threatening. Often, calcium gluconate and muscle relaxers are all that are needed to treat the patient successfully.

These spiders are preyed upon by other animals, especially the Blue Mud Dauber wasp, Chalybion californicum, which occurs throughout the U.S.

Pictures of Latrodectus mactans (Southern Black Widow)

General

Female Spiders

Male Spiders

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